Preheat the oven to 200°C.
Open the oysters carefully and retain their juice.
Melt butter in a pan and cook the chopped shallot gently.
Add vermouth, oyster juice, and stocks, then reduce liquid by two thirds.
Stir in cream and reduce the volume by half.
Place oysters and a little sauce into cleaned shells and bake for 2 minutes.
Whisk mustard, egg yolks, parsley, and half the parmesan into the remaining sauce.
Pour the sauce over the oysters and sprinkle with remaining parmesan.
Boil samphire in salted water for 2 minutes until tender.
Grill the oysters until glazed and serve with the drained samphire.